update_engine: migrate from base::MakeUnique to std::make_unique

base::MakeUnique is being deprecated as we can now use std::make_unique
when compiling code in the C++14 mode.

BUG=chromium:769107
CQ-DEPEND=CL:669672
TEST=Run unit tests.

Change-Id: I82f76647239b1eb3b98b19f6479788ffd86ce756
Reviewed-on: https://chromium-review.googlesource.com/716826
Commit-Ready: Ben Chan <[email protected]>
Tested-by: Ben Chan <[email protected]>
Reviewed-by: Amin Hassani <[email protected]>
Reviewed-by: Sen Jiang <[email protected]>
diff --git a/update_manager/evaluation_context.cc b/update_manager/evaluation_context.cc
index 98238f2..b6c7b91 100644
--- a/update_manager/evaluation_context.cc
+++ b/update_manager/evaluation_context.cc
@@ -24,7 +24,6 @@
 #include <base/bind.h>
 #include <base/json/json_writer.h>
 #include <base/location.h>
-#include <base/memory/ptr_util.h>
 #include <base/strings/string_util.h>
 #include <base/values.h>
 
@@ -229,7 +228,7 @@
 }
 
 string EvaluationContext::DumpContext() const {
-  auto variables = base::MakeUnique<base::DictionaryValue>();
+  auto variables = std::make_unique<base::DictionaryValue>();
   for (auto& it : value_cache_) {
     variables->SetString(it.first->GetName(), it.second.ToString());
   }